package com.linwen.excise.huaweiOJ;

import java.util.Scanner;

/**
 * You are given a rectangular board of M×N squares. Also you are given an unlimited number of standard domino pieces of 2×1 squares.
 * You are allowed to rotate the pieces. You are asked to place as many dominoes as possible on the board so as to meet the following conditions:
 *
 * 1. Each domino completely covers two squares.
 * 2. No two dominoes overlap.
 * 3. Each domino lies entirely inside the board. It is allowed to touch the edges of the board.
 * Find the maximum number of dominoes, which can be placed under these restrictions.
 */
public class _48DominoPiling {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()){
            int m = sc.nextInt();
            int n = sc.nextInt();
            System.out.println(m*n/2);
        }
    }

//    private static int DominoPiling(int m, int n) {
//        if(m==0||n==0) {
//            return 0;
//        }
//        if((m%2==1)&&(n%2==1)){
//            return m*n/2;
//        }
//        return m*n/2;
//    }
}
